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Quality Growing Media

© Kenneth Joergensen

Quality bedding plants require careful selection of potting media, and attention to the way the plugs and pots are subsequently potted and watered. Together, these 3 factors form an integral foundation for successful bedding plant growing. This article, part 1 of 3, deals with the selection of the growing media.

1. Quality Growing Media
2. Quality Potting Techniques
3. Quality Watering Techniques

The Purpose of Growing Media
Indoors, seedlings are grown under luxury conditions: plenty of water and fertilizer, adequate temperatures, and freedom from diseases and insects. These conditions provide for fast growth and high survival rates but increase requirements to the quality of the growing media.

A quality growing media must have certain mechanical and chemical properties. Mechanical properties, detailed in this article series, include providing an anchor for the plants, making oxygen and water available to the roots, and acting as a reservoir for nutrients. Chemical properties include having the proper pH and Caption Exchange Capacities to allow nutrient availability to the plants.

Focus on the Roots
The growing media form the environment in which the roots grow. Plants take up water and dissolved nutrients through small hairs on the roots, and a large well developed root system is required for well performing bedding plants. An ideal growing media must therefore be judged based on it's value to the roots.

Water or Air?
Root hairs are tiny numerous extensions of the roots and they require constant moisture. If exposed to dry air even for a few minutes they die, but on the other hand, they can not withstand being totally immersed in water for too long either. The root hairs take up oxygen and release carbon dioxide continuously, requiring air (gasses) to pass in and out through the growing media; a process called gas exchange.

The ideal environment is thus one which is rich in oxygen and saturated with water vapors. As water uptake and gas exchange take place in the same pore space in the growing media, they are unfortunately also mutually exclusive.

From a mechanical point of view, a growing medium can consist of almost any type of solid material (peat moss sphagnum, vermiculite, sand, etc) as long as it is capable of striking a suitable balance between air and water at the same time. The solids themselves are actually somewhat irrelevant; the interesting properties are the pore spaces which they form. The sizes and shapes of these pore spaces are also referred to as the growing media's "porosity".

Porosity
The pore spaces formed in the growing media will have different sizes and shapes depending on the materials used in the mix.

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